1. Field of the Invention
The present invention relates to isolated polypeptides having alpha-amylase activity and isolated polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides.
2. Description of the Related Art
Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, EC. 3.2.1.1) constitute a group of enzymes which catalyze hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
For a number of years alpha-amylase enzymes have been used for a variety of different purposes, the most important of which are starch liquefaction, textile desizing, starch modification in the paper and pulp industry, and for brewing, ethanol production and baking.
In the case of converting starch into a soluble starch hydrolysate, the starch is depolymerized. The conventional depolymerization process consists of a gelatinization step and two consecutive process steps, namely a liquefaction process and a saccharification process.
Granular starch consists of microscopic granules, which are insoluble in water at room temperature. When an aqueous starch slurry is heated, the granules swell and eventually burst, dispersing the starch molecules into the solution. During this “gelatinization” process there is a dramatic increase in viscosity. As the solids level is 30-40% in a typical industrial process, the starch has to be thinned or “liquefied” so that it can be handled. This reduction in viscosity is today mostly obtained by enzymatic degradation. During the liquefaction step, the long-chained starch is degraded into smaller branched and linear units (maltodextrins) by an alpha-amylase. The liquefaction process is typically carried out at about 105-110° C. for about 5 to 10 minutes followed by about 1-2 hours at about 95° C. The temperature is then lowered to 60° C., a glucoamylase (also known as GA or AMG) or a beta-amylase and optionally a debranching enzyme, such as an isoamylase or a pullulanase are added, and the saccharification process proceeds for about 24 to 72 hours. After saccharification process, the sugar can be converted to ethonal by a fermentation organism, preferably yeast.
It will be apparent from the above discussion that the conventional starch conversion process is very energy consuming due to the different requirements in terms of temperature during the various steps. Processes of conversion of starch without having to gelatinize the starch exist. Such “raw starch” processes are described in U.S. Pat. Nos. 4,591,560, 4,727,026 and 4,009,074, EP Patent No. 0171218 and Danish patent application PA 2003 00949. A polypeptide from Subulispora procurvata having alpha-amylase activity is disclosed in SEQ ID NO: 169 of WO 2006/069290.
It would be advantageous to provide alternative alpha-amylases having different properties than the previously known alpha-amylases, to be used in the starch conversion process so that the overall processes can be combined in one step.